#include <time.h>

#include "log.h"
#include "checksum.h"
#include "tcp_utils.h"
#include "udp_utils.h"
#include "ip4_utils.h"
#include "ip6_utils.h"
#include "gtp_utils.h"
#include "gre_utils.h"
#include "packet_def.h"
#include "packet_utils.h"
#include "packet_layer.h"
#include "packet_parse.h"
#include "packet_craft.h"

#define PACKET_CRAFT_LOG_DEBUG(format, ...) LOG_DEBUG("packet craft", format, ##__VA_ARGS__)
#define PACKET_CRAFT_LOG_ERROR(format, ...) LOG_ERROR("packet craft", format, ##__VA_ARGS__)

struct fingerprint
{
    // TODO
    uint16_t ip_id;
    uint8_t ip_ttl;
    uint16_t tcp_win;
};

static uint8_t append_sender_fingerprint = 0;

/******************************************************************************
 * Private API
 ******************************************************************************/

static inline void calc_packet_fingerprint(struct fingerprint *finger)
{
    if (append_sender_fingerprint)
    {
#define RANGE(rand, start, end) (start + rand % (end - start + 1)) // [start, end]
        struct timespec time;
        clock_gettime(CLOCK_MONOTONIC_COARSE, &time);
        uint64_t random = 0x013579ABCDEF ^ time.tv_nsec;
        finger->ip_id = (uint16_t)(RANGE(random, 32767, 65535));
        finger->ip_ttl = (uint8_t)(RANGE(random, 48, 120));
        finger->tcp_win = (uint16_t)(RANGE(random, 1000, 1460));
    }
    else
    {
        finger->ip_id = 0;
        finger->ip_ttl = 0;
        finger->tcp_win = 0;
    }
}

static void update_udp_hdr(struct udphdr *udp, int trim_len)
{
    uint16_t total = udp_hdr_get_total_len(udp);
    udp_hdr_set_total_len(udp, total - trim_len);
    udp_hdr_set_checksum(udp, 0);
}

static void update_ip4_hdr(struct ip *ip, uint16_t ipid, uint8_t ttl, int trim_len)
{
    int hdr_len = ip4_hdr_get_hdr_len(ip);
    uint16_t total = ip4_hdr_get_total_len(ip);
    ip4_hdr_set_total_len(ip, total - trim_len);
    if (ipid)
    {
        ip4_hdr_set_ipid(ip, ipid);
    }
    if (ttl)
    {
        ip4_hdr_set_ttl(ip, ttl);
    }
    ip->ip_sum = 0;
    ip->ip_sum = checksum((const void *)ip, hdr_len);
}

static void update_ip6_hdr(struct ip6_hdr *ip6, int trim_len)
{
    uint16_t len = ip6_hdr_get_payload_len(ip6);
    ip6_hdr_set_payload_len(ip6, len - trim_len);
}

static void update_gtp1_hdr(struct gtp1_hdr *gtp, int trim_len)
{
    uint16_t msg_len = gtp1_hdr_get_msg_len(gtp);
    gtp1_hdr_set_msg_len(gtp, msg_len - trim_len);
    if (gtp1_hdr_get_seq_flag(gtp) && gtp1_hdr_get_seq(gtp))
    {
        PACKET_CRAFT_LOG_ERROR("crafted packets may be dropped by intermediate devices, the GTPv1 layer requires a sequence number");
    }
}

static void update_gtp2_hdr(struct gtp2_hdr *gtp, int trim_len)
{
    uint16_t msg_len = gtp2_hdr_get_msg_len(gtp);
    gtp2_hdr_set_msg_len(gtp, msg_len - trim_len);
    if (gtp2_hdr_get_seq(gtp))
    {
        PACKET_CRAFT_LOG_ERROR("crafted packets may be dropped by intermediate devices, the GTPv2 layer requires a sequence number");
    }
}

static void update_gre1_hdr(struct gre1_hdr *gre, int trim_len)
{
    uint16_t payload_len = gre1_hdr_get_payload_length(gre);
    gre1_hdr_set_payload_length(gre, payload_len - trim_len);
}

// L2 -- data link layer
// LAYER_PROTO_ETHER: // SKIP
// LAYER_PROTO_PWETH: // SKIP
// LAYER_PROTO_PPP:   // SKIP
// LAYER_PROTO_L2TP:  // TODO ???

// L2 -- tunnel
// LAYER_PROTO_VLAN:  // SKIP
// LAYER_PROTO_PPPOE: // TODO ????
// LAYER_PROTO_MPLS:  // SKIP

// L3 -- network layer
// LAYER_PROTO_IPV4:  // DONE
// LAYER_PROTO_IPV6:  // DONE
// LAYER_PROTO_IPAH:  // TODO ????

// L3 -- tunnel
// LAYER_PROTO_GRE:   // DONE

// L4 -- transport layer
// LAYER_PROTO_UDP:   // DONE
// LAYER_PROTO_TCP:   // DONE
// LAYER_PROTO_ICMP:
// LAYER_PROTO_ICMP6:

// L4 -- tunnel
// LAYER_PROTO_VXLAN: // SKIP
// LAYER_PROTO_GTP_U: // DONE
// LAYER_PROTO_GTP_C:
static void calculate_length_and_checksum(const struct packet *origin_pkt, int layer_count, char *new_pkt_data, uint16_t new_pkt_len, int trim_len)
{
    uint8_t version = 0;
    uint16_t sum = 0;
    char *curr_hdr_ptr = NULL;
    char *last_hdr_ptr = NULL;
    struct tcphdr *tcp = NULL;
    struct udphdr *udp = NULL;
    struct ip *ip4 = NULL;
    struct ip6_hdr *ip6 = NULL;
    struct gtp1_hdr *gtp1 = NULL;
    struct gtp2_hdr *gtp2 = NULL;
    struct gre0_hdr *gre0 = NULL;
    struct gre1_hdr *gre1 = NULL;
    struct raw_layer *curr_layer = NULL;
    struct raw_layer *last_layer = NULL;
    struct fingerprint finger = {};
    calc_packet_fingerprint(&finger);
    for (int i = layer_count - 1; i >= 0; i--)
    {
        curr_layer = (struct raw_layer *)packet_get_raw_layer(origin_pkt, i);
        last_layer = (struct raw_layer *)packet_get_raw_layer(origin_pkt, i + 1);
        curr_hdr_ptr = new_pkt_data + curr_layer->hdr_offset;
        last_hdr_ptr = last_layer ? new_pkt_data + last_layer->hdr_offset : NULL;
        switch (curr_layer->proto)
        {
        case LAYER_PROTO_TCP:
            tcp = (struct tcphdr *)curr_hdr_ptr;
            if (finger.tcp_win)
            {
                tcp_hdr_set_window(tcp, finger.tcp_win);
            }
            tcp_hdr_set_checksum(tcp, 0);
            break;
        case LAYER_PROTO_UDP:
            udp = (struct udphdr *)curr_hdr_ptr;
            update_udp_hdr(udp, trim_len);
            break;
        case LAYER_PROTO_IPV4:
            ip4 = (struct ip *)curr_hdr_ptr;
            if (last_layer && last_layer->proto == LAYER_PROTO_TCP)
            {
                tcp = (struct tcphdr *)last_hdr_ptr;
                tcp->th_sum = checksum_v4(tcp, new_pkt_len - last_layer->hdr_offset, IPPROTO_TCP, &ip4->ip_src, &ip4->ip_dst);
            }
            if (last_layer && last_layer->proto == LAYER_PROTO_UDP)
            {
                udp = (struct udphdr *)last_hdr_ptr;
                udp->uh_sum = checksum_v4(udp, new_pkt_len - last_layer->hdr_offset, IPPROTO_UDP, &ip4->ip_src, &ip4->ip_dst);
            }
            update_ip4_hdr(ip4, finger.ip_id, finger.ip_ttl, trim_len);
            break;
        case LAYER_PROTO_IPV6:
            ip6 = (struct ip6_hdr *)curr_hdr_ptr;
            if (last_layer && last_layer->proto == LAYER_PROTO_TCP)
            {
                tcp = (struct tcphdr *)last_hdr_ptr;
                tcp->th_sum = checksum_v6(tcp, new_pkt_len - last_layer->hdr_offset, IPPROTO_TCP, &ip6->ip6_src, &ip6->ip6_dst);
            }
            if (last_layer && last_layer->proto == LAYER_PROTO_UDP)
            {
                udp = (struct udphdr *)last_hdr_ptr;
                udp->uh_sum = checksum_v6(udp, new_pkt_len - last_layer->hdr_offset, IPPROTO_UDP, &ip6->ip6_src, &ip6->ip6_dst);
            }
            update_ip6_hdr(ip6, trim_len);
            break;
        case LAYER_PROTO_GTP_C: /* fall through */
        case LAYER_PROTO_GTP_U:
            version = peek_gtp_version(curr_hdr_ptr, curr_layer->hdr_len);
            if (version == 1)
            {
                gtp1 = (struct gtp1_hdr *)curr_hdr_ptr;
                update_gtp1_hdr(gtp1, trim_len);
            }
            if (version == 2)
            {
                gtp2 = (struct gtp2_hdr *)curr_hdr_ptr;
                update_gtp2_hdr(gtp2, trim_len);
            }
            break;
        case LAYER_PROTO_GRE:
            version = peek_gre_version(curr_hdr_ptr, curr_layer->hdr_len);
            if (version == 0)
            {
                gre0 = (struct gre0_hdr *)curr_hdr_ptr;
                if (gre0_hdr_get_checksum_flag(gre0))
                {
                    gre0_hdr_set_checksum(gre0, ntohs(0));
                    sum = checksum((const void *)curr_hdr_ptr, new_pkt_len - curr_layer->hdr_offset);
                    gre0_hdr_set_checksum(gre0, ntohs(sum));
                }
            }
            if (version == 1)
            {
                gre1 = (struct gre1_hdr *)curr_hdr_ptr;
                update_gre1_hdr(gre1, trim_len);
            }
            break;
        default:
            break;
        }
    }
}

/******************************************************************************
 * Public API
 ******************************************************************************/

void append_sender_fingerprint_to_crafted_packet()
{
    append_sender_fingerprint = 1;
}

/*
 * tcp_seq: the sequence number of the new TCP packet (in host byte order)
 * tcp_ack: the acknowledgment number of the new TCP packet (in host byte order)
 * tcp_options_len: the length of the options (must be a multiple of 4)
 */
struct packet *craft_tcp_packet(const struct packet *origin_pkt, uint32_t tcp_seq, uint32_t tcp_ack, uint8_t tcp_flags,
                                const char *tcp_options, uint16_t tcp_options_len,
                                const char *tcp_payload, uint16_t tcp_payload_len)
{
    // check arguments
    if (origin_pkt == NULL ||
        (tcp_options == NULL && tcp_options_len != 0) || (tcp_options != NULL && tcp_options_len == 0) ||
        (tcp_payload == NULL && tcp_payload_len != 0) || (tcp_payload != NULL && tcp_payload_len == 0) ||
        (tcp_options_len && tcp_options_len % 4 != 0))
    {
        PACKET_CRAFT_LOG_ERROR("craft TCP packet failed, invalid arguments");
        return NULL;
    }

    // check the innermost layer of the original packet
    int layer_count = packet_get_layer_count(origin_pkt);
    const struct raw_layer *tcp_layer = packet_get_raw_layer(origin_pkt, layer_count - 1);
    if (tcp_layer == NULL || tcp_layer->proto != LAYER_PROTO_TCP)
    {
        PACKET_CRAFT_LOG_ERROR("craft TCP packet failed, the innermost layer of the original packet is not TCP");
        return NULL;
    }

    // calculate the new packet length
    int trim_len = tcp_layer->hdr_len + tcp_layer->pld_len - tcp_options_len - tcp_payload_len - sizeof(struct tcphdr);
    uint16_t new_pkt_len = origin_pkt->data_len - origin_pkt->trim_len - trim_len;
    struct packet *new_pkt = packet_new(new_pkt_len);
    if (new_pkt == NULL)
    {
        PACKET_CRAFT_LOG_ERROR("craft TCP packet failed, no space to allocate new packet");
        return NULL;
    }

    // copy the data to the new packet
    char *new_pkt_data = (char *)packet_get_raw_data(new_pkt);
    memcpy(new_pkt_data, packet_get_raw_data(origin_pkt), tcp_layer->hdr_offset + sizeof(struct tcphdr));
    if (tcp_options_len)
    {
        memcpy(new_pkt_data + tcp_layer->hdr_offset + sizeof(struct tcphdr), tcp_options, tcp_options_len);
    }
    memcpy(new_pkt_data + tcp_layer->hdr_offset + sizeof(struct tcphdr) + tcp_options_len, tcp_payload, tcp_payload_len);
    struct tcphdr *hdr = (struct tcphdr *)(new_pkt_data + tcp_layer->hdr_offset);
    tcp_hdr_set_seq(hdr, tcp_seq);
    tcp_hdr_set_ack(hdr, tcp_ack);
    tcp_hdr_set_flags(hdr, tcp_flags);
    tcp_hdr_set_hdr_len(hdr, sizeof(struct tcphdr) + tcp_options_len);

    calculate_length_and_checksum(origin_pkt, layer_count, new_pkt_data, new_pkt_len, trim_len);

    packet_parse(new_pkt, new_pkt_data, new_pkt_len);
    memcpy(&new_pkt->meta, &origin_pkt->meta, sizeof(struct metadata));
    new_pkt->meta.origin_ctx = NULL;

    return new_pkt;
}

struct packet *craft_udp_packet(const struct packet *origin_pkt, const char *udp_payload, uint16_t udp_payload_len)
{
    // check arguments
    if (origin_pkt == NULL || (udp_payload == NULL && udp_payload_len != 0) || (udp_payload != NULL && udp_payload_len == 0))
    {
        PACKET_CRAFT_LOG_ERROR("craft UDP packet failed, invalid arguments");
        return NULL;
    }

    // check the innermost layer of the original packet
    int layer_count = packet_get_layer_count(origin_pkt);
    const struct raw_layer *udp_layer = packet_get_raw_layer(origin_pkt, layer_count - 1);
    if (udp_layer == NULL || udp_layer->proto != LAYER_PROTO_UDP)
    {
        PACKET_CRAFT_LOG_ERROR("craft UDP packet failed, the innermost layer of the original packet is not UDP");
        return NULL;
    }

    // calculate the new packet length
    int trim_len = udp_layer->hdr_len + udp_layer->pld_len - udp_payload_len - sizeof(struct udphdr);
    uint16_t new_pkt_len = origin_pkt->data_len - origin_pkt->trim_len - trim_len;
    struct packet *new_pkt = packet_new(new_pkt_len);
    if (new_pkt == NULL)
    {
        PACKET_CRAFT_LOG_ERROR("craft UDP packet failed, no space to allocate new packet");
        return NULL;
    }

    // copy the data to the new packet
    char *new_pkt_data = (char *)packet_get_raw_data(new_pkt);
    memcpy(new_pkt_data, packet_get_raw_data(origin_pkt), udp_layer->hdr_offset + sizeof(struct udphdr));
    memcpy(new_pkt_data + udp_layer->hdr_offset + sizeof(struct udphdr), udp_payload, udp_payload_len);

    calculate_length_and_checksum(origin_pkt, layer_count, new_pkt_data, new_pkt_len, trim_len);

    packet_parse(new_pkt, new_pkt_data, new_pkt_len);
    memcpy(&new_pkt->meta, &origin_pkt->meta, sizeof(struct metadata));
    new_pkt->meta.origin_ctx = NULL;

    return new_pkt;
}

struct packet *craft_l3_packet(const struct packet *origin_pkt, uint8_t ip_proto, const char *l3_payload, uint16_t l3_payload_len)
{
    if (origin_pkt == NULL || (l3_payload == NULL && l3_payload_len != 0) || (l3_payload != NULL && l3_payload_len == 0))
    {
        PACKET_CRAFT_LOG_ERROR("craft L3 packet failed, invalid arguments");
        return NULL;
    }

    int i = 0;
    int layers = packet_get_layer_count(origin_pkt);
    const struct raw_layer *l3_layer = NULL;
    for (i = layers - 1; i >= 0; i--)
    {
        l3_layer = packet_get_raw_layer(origin_pkt, i);
        if (l3_layer->proto == LAYER_PROTO_IPV4 || l3_layer->proto == LAYER_PROTO_IPV6)
        {
            break;
        }
        else
        {
            l3_layer = NULL;
        }
    }
    if (l3_layer == NULL)
    {
        PACKET_CRAFT_LOG_ERROR("craft L3 packet failed, the original packet does not contain an IP layer");
        return NULL;
    }

    // calculate the new packet length
    // trim IPv4 options
    // trim IPv6 extension headers
    int l3_hdr_len = l3_layer->proto == LAYER_PROTO_IPV4 ? sizeof(struct ip) : sizeof(struct ip6_hdr);
    int trim_len = l3_layer->hdr_len + l3_layer->pld_len - l3_payload_len - l3_hdr_len;
    uint16_t new_pkt_len = origin_pkt->data_len - origin_pkt->trim_len - trim_len;
    struct packet *new_pkt = packet_new(new_pkt_len);
    if (new_pkt == NULL)
    {
        PACKET_CRAFT_LOG_ERROR("craft L3 packet failed, no space to allocate new packet");
        return NULL;
    }

    // copy the data to the new packet
    char *new_pkt_data = (char *)packet_get_raw_data(new_pkt);
    memcpy(new_pkt_data, packet_get_raw_data(origin_pkt), l3_layer->hdr_offset + l3_hdr_len);
    if (l3_payload)
    {
        memcpy(new_pkt_data + l3_layer->hdr_offset + l3_hdr_len, l3_payload, l3_payload_len);
    }
    // update ip_proto
    if (l3_layer->proto == LAYER_PROTO_IPV4)
    {
        struct ip *ip4 = (struct ip *)(new_pkt_data + l3_layer->hdr_offset);
        ip4_hdr_set_protocol(ip4, ip_proto);
    }
    else
    {
        struct ip6_hdr *ip6 = (struct ip6_hdr *)(new_pkt_data + l3_layer->hdr_offset);
        ip6_hdr_set_next_header(ip6, ip_proto);
    }
    calculate_length_and_checksum(origin_pkt, i + 1, new_pkt_data, new_pkt_len, trim_len);

    packet_parse(new_pkt, new_pkt_data, new_pkt_len);
    memcpy(&new_pkt->meta, &origin_pkt->meta, sizeof(struct metadata));
    new_pkt->meta.origin_ctx = NULL;

    return new_pkt;
}